


Ectothermy

by WolffyLuna



Category: Undertale (Video Game)
Genre: Bathing/Washing, Cold, F/F, Fluff, Romantic Fluff, Strip Tease
Language: English
Status: Completed
Published: 2016-02-06
Updated: 2016-02-06
Packaged: 2018-05-18 12:31:54
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,277
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5928439
Author URL: https://archiveofourown.org/users/WolffyLuna/pseuds/WolffyLuna
Summary: <blockquote class="userstuff">
              <p>Alphys, as a dinosaur monster, is warm blooded. Undyne, as a fish monster, isn't. </p>
<p>Their first cold day on the surface is... interesting.</p>
            </blockquote>





	Ectothermy

Alphys lay down in front of the heater, fighting an abstract to death on her laptop. The first really cold day of autumn had arrived. She lifted her head from her report, and looked out the window. Red leaves from the maple tree covered their courtyard’s lawn,and frost covered the leaves. Fog curled around at the base of the tree. She waited for Undyne to come back from her early morning soccer practice (She’d fallen in love with the human sport, and had started coaching Frisk’s team.)

She broke out of her reverie, turned back to the computer, and bit her lip. The abstract just went on too long, and she couldn’t think of a way to fit in a summary of the results. She deleted the offending sentences and started again. _Fire based monsters, and monsters that resemble mammals, birds and dinosaurs appear to be endothermic, while skeletons and--_ She stopped mid sentence, and checked the word count. Nope, still too long. She cut the sentences, and decided to proofread the discussion again.

The door opened, and then there was a thud.

Alphys jumped up.

Undyne crawled along the floor, shivering and looking dazed.

“U-undyne, are you alright?!”

Undyne mumbled. “--too darn cold. It’s as bad as Snowdin. Couldn’t get anything done there either.”

Alphys had a brainwave. “Undyne, are fish cold blooded?”

“... I’m not a fish. I’m a monster. A REALLY TIRED, COLD BLOODED MONSTER.”

Alphys quickly scrawled that on a sticky note, before the implications of what Undyne said hit her. Undyne had been out in near zero temperatures, wearing only a short sleeved ref’s top. ““O-oh no, we have to get you warmed up!” She put the laptop on a table, and dragged Undyne out of the tiled atrium, and put her next to the heater. “Stay h-here! I’ll make you some tea! A-and run a bath!”

“Iiiii’ll be fiiinne.” Undyne’s words slurred and drawled.

Alphys' put the back of her hand on Undyne’s forehead, and jerked it away. “Y-you’re freezing! I can’t let you stay this cold!” Alphys ran into the kitchen. She took the kettle off it’s base, and fumbled with its top until she got it open. She filled it up, closed it, put it back on the base and flicked the switch. She grabbed Undyne’s favourite tea (she had to get up on tip toes) and a mug. She set them next to the kettle.

She then ran out of the kitchen, up the stairs and into the bathroom. She slammed the bathroom door open, and skidded over to bath. She turned on the taps, and messed around til they were just the right temperature. She put the plug in, and ran back to the kitchen to check on the kettle.

Not ready yet.

She sprinted back up the stairs to check on the bath. Not ready either. She raced back down to the kitchen. She stopped in front if the kitchen door, panting and trying to catch her breath. She regretted spending so much time in front of the heater now. She sweated, and she felt like her insides were about to boil from all the running

“You don’t have to ruun aarroouundd...” Undyne slurred her words a little less. She was sitting up, and looking less dazed as well, so that was good.

“But you’re half frozen!... I w-want to look after you too. You l-look after me...”

Undyne smiled big and broad. “Alright, I’m prepared to be looked after. JUST THIS ONCE, PUNK.”

Alphys laughed. The kettle clunked as it finished boiling, and she bustled in. She poured the water into a mug, placed the tea bag, and brought it Undyne.

Undyne grabbed it out of her hands, and nearly drank it in one gulp. She didn’t even let it brew. Undyne sighed. “Oh my, that’s good...”

“I-i better go check on the bath.” Alphys ran back up the stairs. Warm water filled the bath, and steam settled over the floor and fogged up the mirrors. She sticks a clawed finger in. Just the right temperature: hot, but just as hot as you can stand, no more. She turned off the taps, and went back to Undyne. “The bath’s r-ready now.”

Undyne reached up to put her mug on the table, and dragged herself up. She teetered up the stairs, leaning heavily on the railing.

Alphys followed behind, hoping she wouldn’t have to try and catch Undyne.

The bathroom was steamier and warmer than it was when Alphys' had turned off the tap. The water condensed on her glasses, and she had to take them off and put them next to the sink.

Undyne sat down clumsily on the bath mat. She pulled of her black and white singlet, crossing her arms over her hip and lifting the hem up and over her head. Fat and muscle scrunched around her sides, and her lateral line curled in an elegant s-shape up her waist and ribs. Her abs were defined, not as six pack with each clear, but with an indent around all of them.

Alphys’ caught herself staring, and tried to look away, before remembering _Undyne was her girlfriend,_ and she was totally allowed ogle. (It still felt odd to think of Undyne as her girlfriend, even after all this time.)

Undyne noticed Alphys staring, and grinned evilly. She reached around to her back to unhook her sports bra, failed, and had to pause the impromptu show to work out what went wrong. Alphys just watched, rapt, at the way Undyne’s arms flexed as she struggled with the hooks. Then the, undone, the band started to pull apart and fall away. Her breast dropped a little as the support went away, in a way that Alphys’ found more distracting than her arms. She slipped the straps off her shoulders, and took it off properly. Her breasts dropped all the way.

Heat went up from Alphys' cheeks to her crest. (And other... places as well, she’d admit.)

Undyne pulled her pants down off her hips, slowly, teasingly, then got the waistband stuck under her butt. She shuffled back and forward, trying to unstick it.

Alphys giggled, and so did Undyne.

Then the pants were off, and so was the underwear. Undyne stood up, and stepped into the bath (much more coordinated than she was before, so that was good.) She sighed, and slid down till her chin was just out of the water.

Alphys sat on the side of the bath, and they sat together quietly.

A few minutes later, Undyne got a gleam in her eye.

“Uh, Undyne?”

Undyne grinned, showing off sharp, pointed teeth.

“Undyne?”

Undyne lunged forward, and grabbed Alphys in a headlock. “ALPHYS!” She pulled Alphys into the bath.

Alphys yelped. She couldn’t tell whether she should be surprised or outraged. “What was that?”

Undyne nuzzled Alphys’ forehead. “A bath’s the best way to relax after running round a lot, wouldn’t you say?

Alphys sighed, and settled into the water.

“Also, now your clothes are all wet, and you’ll have to get out of them.” Her grinned turned lecherous

Alphys gave Undyne a sideways look.

“Hey, it’s only fair! You got to ogle _me._ ”

Alphys smiled, and started to strip off, trying to stay in the warm water as much as possible.

“If this is what happens when I freeze my ass off, I’m going to have to start chilling myself deliberately.”

“H-how about I only do this when you’ve kept yourself warm.”

Undyne kissed Alphys cheek. “You drive a hard bargain, but I’ll accept. Especially if I get to snuggle in the bath with you.”

Alphys blushed, and kissed Undyne back.


End file.
